This application claims the priority of German Application No. 100 57 699.0 filed Nov. 21, 2000, which is incorporated herein by reference.
This invention relates to an apparatus for measuring the tension of sliver composed of cotton fibers, chemical fibers or the like, as it runs in a draw frame. Upstream of the draw frame a creel is situated below which coiler cans are positioned from which sliver is withdrawn. Downstream of the creel, as viewed in the direction of sliver advance, a rider roll assembly and a sliver guide with transporting rolls are provided, followed downstream by input rolls of the draw unit of the draw frame. The slivers running into the draw frame from the coiler cans are in a tensioned condition at least in the zone between the transport rolls and the input rolls of the draw unit.
The sliver tension effected by the transport rolls is derived from the ratio of the circumferential speed of the lower input roll of the draw unit to the circumferential speed of the transport rolls. A setting of the transport roll tension is feasible by means of the transmission gearing associated with the transport rolls. The transport roll tension should be set in such a manner that the slivers between the transport rolls and the lower input roll of the draw unit run with the smallest possible tension which still ensures that the slivers do not undulate as they run on the sliver guide table. Further, when setting the tension, it should be taken into consideration that a satisfactory spread of the sliver is ensured. The tension setting is based on a table in which the different transmission gears are associated with a respective transport roll tension; such table is based empirically for different fiber materials. For the same transmission gear a different transport roll tension may result in case an assortment (fiber lot) change occurs. In practice, the run of the slivers is visually observed and based on such observation, an appropriate transmission gear is selected. In addition, the quality of the drafted sliver at the output of the draw unit is taken into consideration.
It is a disadvantage of the above-outlined conventional arrangement that the tension setting requires substantial experience and does not make possible a precise determination of the transport roll tension.
It is an object of the invention to provide an improved apparatus of the above-outlined type from which the discussed disadvantages are eliminated and which, in particular, makes possible a precise determination of the transport roll tension and a setting for different fiber lots.
This object and others to become apparent as the specification progresses, are accomplished by the invention, according to which, briefly stated, the draw frame includes a transport roll pair for simultaneously guiding a plurality of slivers running in an advancing direction; and a series of drafting roll pairs spaced from one another in the advancing direction. One of the drafting roll pairs is a first drafting roll pair as viewed in the advancing direction. The first drafting roll pair is positioned downstream of the transport roll pair. A measuring device is contacted by the running slivers and includes a pressure-sensitive member exposed to a force derived from the running slivers for emitting,a signal representing the force; and a deflecting arrangement for deflecting the running slivers for causing them to be partially trained about the deflecting arrangement to exert to the pressure-sensitive member a pressing force proportional to a tension of the slivers prevailing upstream and downstream of the pressure-sensitive member.
The measures according to the invention make possible a precise determination particularly of the transport roll tension and thus provide for an optimal setting of such tension even in case of a fiber lot change. In this manner, tension values are determined for the most important materials. Therefore, the actual measured value for the tension draft may be compared with the determined, desired value and the machine operator may receive an indication whether the correct tension values have been selected.